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The control of pulsed current gas metal arc (GMA) welding is highly critical owing to the simultaneous influence of the pulse parameters on thermal and metal transfer behaviours of the process. An analytical model has been developed to provide a theoretical understanding of the influence of pulse parameters on the behaviour of metal transfer and thermal characteristics in pulsed current GMA welding using Al-Mg filler wire. The variations in thermal and metal transfer behaviours with changes in pulse parameters have been satisfactorily analysed considering a summarised influence of pulse parameters defined by a dimensionless factor w5(I b /I p )ft b , proposed previously. A large number of process parameters have been considered, as a result of using four different GMA welding power sources. The hypothesis has been verified using some previously reported experimental results. The theoretical model may be useful in the control of pulse parameters to achieve desired behaviours of thermal and metal transfer under different conditions of weld fabrication, thereby facilitating more universal application of GMA welding. List of symbolsa acceleration of droplet due to plasma aerodynamic drag force, m s 22 A s total surface area of molten metal transferred per pulse, m 2 A w cross-sectional area of filler wire, m 2 C p specific heat of argon plasma510 4 J kg 21 K 21 C p(l) specific heat of liquid filler metal5 1130 J kg 21 K 21 C p(s) specific heat of solid filler metal5 1049 J kg 21 K 21 D diameter of droplets, m E w electrode extension520610 23 m f pulse frequency H A heat input due to arc heating, J s 21 H cv convective heat loss per unit mass of filler metal during flight from tip of filler wire to weld pool, J kg 21 H de heat content per unit mass of droplet at time of deposition, J kg 21 H dp heat content of total weld metal deposited per pulse, kJ H i heat content per unit mass of molten metal during its detachment from electrode, J kg 21 H O heat generated at tip of electrode per unit time, J s 21 H r radiative heat loss per unit mass of filler metal during flight from tip of filler wire to weld pool, J kg 21 H R heat input due to resistive heating, J s 21 H tl total heat loss during flight of molten metal transferred per pulse, kJ H w heat absorbed by filler wire per unit time, J s 21 I b base current, A I eff effective current, A I m mean current, A I p peak current, A j eff effective current density at tip of electrode, A m 22 j g current density of plasma in arc column, A m 22 j m mean current density at tip of electrode, A m 22 l arc length50 . 01 m L latent heat of filler wire53 . 97610 5 J kg 21 M t mass of filler wire transferred per pulse, kg N d number of molten filler metal droplets transferred per pulse N u Nusselt number P r Prandtl number r effective radius, m R resistance of electrode extension, V R e Reynolds number R O resistivity of filler wire50 . 25610 26 V m Science and Technology of Welding and Joining 2006 VOL 11 NO 2232 R w radius of filler wire50 . 8610 23 m t total pulse time t b base cur...

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The microstructure and cast morphology of pulsed-current gas-metal arc (GMA) weld deposit of 1.6-mm-diameter aluminum (ER1100) and Al-Mg alloy (ER5183) filler wire have been studied on similar base material. The effect of the influence of the pulse frequency taken together with the peak and background currents and their durations, as defined by a dimensionless factor /, varied in the range of 0.05 to 0.4 on the solidification behavior of the weld metal with respect to the morphology of its cast microstructure has been studied. The morphology of the dendrite as revealed under the scanning electron microscope (SEM) has been studied in reference to the change in the length of its coaxial growth, its aspect ratio, and its primary arm spacing, related to the variation in the factor /. It is shown that the microstructure of the weld metal changes significantly with the change in the factor /. It is also found that the variation in the mean current and heat input significantly affects the morphology of the dendrite, as defined here. The morphological characteristics of the dendrites have been correlated to the factor /, the mean current, and the heat input. The dendrite arm spacing has been found to maintain a good correlation with the estimated cooling rate of the weld metal, in that it decreases with the increase in the cooling rate. At a given heat input, mean current, and /, the Al-Mg alloy contains a comparatively larger fraction of finer dendrites with an appropriately similar morphology than does the aluminum weld deposit.

A summarized influence of pulse parameters have been studied; these parameters are defined by a hypothetically derived factor / = [(I b /I p )ft b ] on the characteristics of bead-on-plate weld deposits of aluminum and Al-Mg alloy, with respect to their geometry and microstructure. The weld geometry has been studied in reference to the depth, width, and area of fusion of the base plate, and the bead height, bead width, toe angle, form factor, area of weld deposit, fraction of base metal fusion per unit mass of weld deposition, and dilution. It is found that these aspects of geometry and the microstructure of the weld metal and heat-affected zone (HAZ) vary significantly with a change in the factor /. The value of the factor / at approximately 0.1 has been seen as critical to the change in the different aspects of the pulsed-gas metal arc (P-GMA) weld. It is also found that, at a given /, the variation in mean current and heat input significantly affects the geometry and microstructure of the weld deposit.